The long-term objective of this research is to understand how dendritic cell (DC) subsets regulate the induction of anti-viral helper T (Th) cells and cytotoxic T cells (CTL) and how this regulation impacts clearance of a simple, well characterized RNA virus, vesicular stomatitis virus (VSV). Priming for recall CTL responses to VSV is dependent on the presence of CD4+ Th cells as well as macrophages and marginal dendritic cells (MDC), a phagocytic DC subset localized in the marginal zones of the spleen. Red pulp macrophages (RPM) and MDC have been previously implicated as important cell types for efficient Th cell and CTL priming because splenic re-population by RPM and MDC following liposome-mediated elimination of phagocytic cells is associated with restoration of priming competency. Interestingly, interdigitating dendritic cells (IDC) remain intact following this treatment and this DC subset processes and presents VSV peptide/MHC class I and II complexes in vivo in a macrophage/MDC independent fashion. Despite the display of viral peptides, IDC induce a weak primary anti-VSV IL-2 and IFN-gamma cytokine response in vivo; whereas, the IL-4 cytokine response remains relatively intact. Based on these studies, we hypothesize that IDC drive Th0-Th2 differentiation and thereby regulate the protective humoral immune response to this virus. We further postulate that MDC induce Th0-Thl maturation and are therefore primarily responsible for generating a cell mediated immune response. The studies proposed in Aim l will test the validity of this paradigm by characterizing the primary anti-VSV Thl and Th2 cytokine response in situ driven by IDC. The proposed studies will utilize a multiprobe RNase protection assay so that multiple cytokines can be quantitated in a single sample. ELISPOT assays will verify that the cytokine mRNAs are translated. Chemokine/cytokine profiles of IDC, MDC and distinct mp subpopulations will be further defined by gene array analysis because of their potential role in recruitment of precursor VSV Th cells and inflammatory cells required for viral clearance. In Aim 2 discrete biological properties of IDC related to antigen presenting function are examined to gain insight into the mechanistic basis for the preferential activation and maturation of Th2 cells. In Aim 3 we propose to assess the immune competency of VSV-specific CDS+ T cells that have engaged VSV-infected IDC during the priming event. This will be achieved with a novel adoptive transfer model in combination with an aliphatic marker, so that clonal growth, CTL effector function, cytokine profile and memory development of VSV-specific T cells can be examined at the single cell level.